The aim of the proposed research is to measure the impact, in normal infants within the peak age for SIDS (3 mos), of mother-infant cosleeping on infant sleep and arousal patterns, respiration thermoregulation and cardiac activity. This proposal emerges from both (1) evolutionary and cross-cultural evidence that parent-infant cosleeping is the more appropriate context in which to appreciate the normal development of infant sleep, and (2) current hypotheses concerning the role of environmental factors and arousal deficiency in the pathogenesis of Sudden Infant Death. The accepted research model for studying the development of infant sleep reflects urban Western culture's practice of solitary sleeping infants. This model neglects the evolutionary context of parent-infant cosleeping in which the neural structures controlling sleep physiology evolved. It can be argued that parent-infant cosleeping may provide an adaptive, sensory rich environment to which the developing infant is responsive and, in some cases, possibly dependent for survival: The sensory environment of cosleeping could be critical to particularly vulnerable infants in their ability to respond to or circumvent a life threatening-event in sleep. A three consecutive night polysomnographic study is proposed where mother-infant pairs alternate between sleeping together and apart. All procedures are non-invasive. Infant sleep pattern, arousals, respiration pattern including frequency and duration of breathing pauses, skin temperature, and cardiac activity in solitary vs. cosleeping conditions will be compared using parametric statistical procedures. Physiological interactions between cosleepers also will be investigated by coherence analysis of respiration and cardiac activity in infants and mothers and measurement of cardiac R-R interval variability. Particular emphasis will be placed on quantification of arousals in sleep in view of both (1) preliminary data demonstrating more frequent and simultaneous arousals in infant-mother pairs while cosleeping, and (2) recent hypotheses about the role of arousal deficiency in the pathogenesis of SIDS. The results of this study could present a challenge to the accepted model of studying infants sleeping in isolation. This research may also document non-trivial physiological interactions between infants and mothers while cosleeping which could be relevant to current hypotheses on the etiology and avoidance of Sudden Infant Death.